Method and plant for recovering heat from smoke gases

Abstract

A method and plant for recovering heat from smoke gases in combustion plants, whereat the combustion air is compressed prior to being supplied to the combustion chamber of the plant. The compressed smoke gases from the combustion chamber are cooled, at a pressure which exceeds 1.5 atmospheres, to a temperature beneath 100° C., preferably beneath 80° C., and are then caused to expand in a turbine, whereat the energy released by said expansion is utilized for compressing the air of combustion. The plant comprises one or more compressors (2) which are arranged upstream of the combustion chamber (6) of the combustion plant and which compress the air of combustion; and a turbine (9) arranged downstream of the combustion chamber or chambers (6) for expanding the compressed smoke gases. The turbine (9) is mechanically connected to an associated compressor (2), so that the kinetic energy developed by the turbine through expansion of the smoke-gases is utilized in the compressor (2) for compressing the air of combustion. Connected between the last combustion chamber (6) in the system and the turbine (9) is a smoke-gas cooler (7,8) which works at a smoke-gas pressure exceeding 1.5 atmospheres and in which the smoke gases are cooled to a temperature which is lower than 100° C., preferably lower than 80° C.

We claim: 
     
       1. A method of recovering heat from smoke gases in a combustion plant comprising the steps of compressing air for combustion to a first intermediate pressure in a first compressor, then compressing the air to a second higher pressure in a second compressor, passing the air at said second higher pressure to a combustion chamber, burning a combustible fuel containing water in the presence of said air at said second higher pressure in the combustion chamber to produce smoke gases containing water vapor at substantially said second higher pressure, passing said smoke gases at said second higher pressure through a first turbine to drive the turbine and reduce the pressure of said smoke gases to a second intermediate pressure, said first turbine being connected to said second compressor for driving the same, thereafter condensing water vapor in said smoke gases at said second intermediate pressure to regain the heat of vaporazation of the water vapor in the smoke gases, and then passing said smoke gases through a second turbine to drive the turbine and reduce the pressure of said smoke gases to atmospheric pressure, said second turbine being connected to said first compressor for driving the same. 
     
     
       2. A combustion plant for recovering heat from smoke gases comprising first and second compressor means connected in series to raise the pressure of combustion air from atmospheric pressure to a first intermediate pressure and thence to a second higher pressure, at least one combustion chamber means operatively connected to said second compressor means for burning fuel containing water in the presence of said combustion air for producing compressed smoke gases at substantially said second higher pressure; a first turbine means operatively connected to said combustion chamber and said second compressor for receiving said compressed smoke gases and reducing the pressure thereof to a second intermediate pressure thereby converting the pressure of the smoke gases to mechanical energy driving said second compressor means; condenser means connected to said first turbine for receiving the expanded smoke gases therefrom and recapturing the heat of evaporation from the water vapor in said gases; and a second turbine means operatively connected to said condenser means and said first compressor for receiving the expanded smoke gases from said condenser means and reducing the pressure thereof to atmospheric while converting the pressure of the smoke gases to mechanical energy driving said first compressor means. 
     
     
       3. A combustion plant as defined in claim 2 wherein said condenser includes means for regulating the cooling effect produced therein on said smoke gases and permitting control of the smoke gas temperature downstream of the condenser at a relatively constant temperature regardless of variations in the heat output of said combustion chamber. 
     
     
       4. A combustion plant as defined in claim 2 including at least two combustion chamber means, one of which is nearest the condenser means in the direction of gas flow and is adapted to be operated at a varying load whereby the temperature of the smoke gases downstream of the cooler may be maintained substantially constant irrespective of variations in the heat output of the plant. 
     
     
       5. A combustion plant as defined in claim 4 wherein said condenser means comprises means for cooling the smoke gases from the first turbine to a temperature which is lower than 1.2 times the temperature of the cooling medium used in the condenser, expressed in degress Kelvin. 
     
     
       6. A combustion plant as defined in claim 4 including a third compressor means connected in series between said first and second compressor means and a third turbine means operatively connected between said first and second turbines and to said third compressor means for driving the same. 
     
     
       7. A combustion plant as defined in claim 4 including at least one compressor and turbine connected in parallel to one of said first and second compressors and turbines respectively. 
     
     
       8. A combustion plant as defined in claim 2 wherein said condenser means comprises means for heating a supply of water. 
     
     
       9. The method of recovering heat from smoke gases in a combustion plant comprising the steps of compressing air for combustion in at least one compressor to a pressure substantially above atmospheric pressure, combusting fuel in the presence of said compressed air to produce smoke gases containing water vapor having a temperature in the range of about 600° C. to 800° C., thereafter condensing the water vapor in said smoke gases in a heat-exchanger/condenser to reduce the temperature of said smoke gases to between 50° C. and 100° C. while transferring heat, including regained heat of vaporatization, to water flowing in said heat-exchanger/condenser, and thereafter expanding the gases in a turbine connected to said compressor to mechanically drive the compressor and reduce the pressure and temperature of the smoke gases to substantially atmospheric temperature and pressure.